The invention relates generally to automotive vehicle suspension systems and more specifically, to a combination traction bar, chassis lifting device and suspension modifying device for four-wheel drive off road vehicles having leaf spring suspension.
In four-wheel drive vehicles used for heavy duty work such as off road transportation, snow plowing, or the like, it is common to fit the suspension of these vehicles with various spacing devices which raise the chassis of the vehicle for achieving greater ground clearance and allowing the use of larger traction improving tires. However, a problem attendant with the use of these various spacing devices and larger tires is increased axle wrap-up or wheel hop during rapid acceleration or deceleration of the vehicle. Axle wrap-up about the leaf spring of the vehicle can deleteriously effect the handling and steering of the vehicle. However, an even more serious problem occurs under maximum acceleration or the application of maximum braking force when the wheels of the vehicle are lifted by axle wrap-up to such an extent as to lose traction or spin, setting up a recurrent periodic lifting and dropping of the effected wheel which is commonly referred to as wheel hop. Not only is this phenomenon damaging to the tire surface, the drive train and the differential gearing, but acceleration or deceleration is degraded and the steering control of the vehicle is poor due to the uncentered forward thrust or rearward thrust generated by the effected wheel and due to the cyclic character of the impulse exerted by such an effected wheel. These problems are increased when spacing devices and larger tires are employed since the larger tires provide increased traction and the diameter of the tires provides an increased moment on the axle of the vehicle. Furthermore, the spacing devices themselves increase the moment felt by the vehicle leaf spring.
Heretofore, numerous approaches have been followed in modifying suspension systems employing leaf springs for various purposes. One prior art construction for preventing spring wrap-up in drag racing cars involve the mounting of a relatively rigid beam forwardly directed under each rear leaf spring of the vehicle. The rear and forward ends of the beam are pivotally secured to the axle housing and to the vehicle frame, respectively. Such a pivotally mounted beam is commonly referred to in the drag racing art as a radius rod type of traction bar. This arrangement compels the axle housing to swing about the forward pivot and thus prevents axle wrap-up about the leaf spring. Such devices can even be found with flexible beams or radius rods. However, these devices somewhat impair the ride of the vehicle and in the drag racing context, fail to compensate for the transfer of vehicle weight to one rear wheel mainly due to the torque reaction of the motor and fail to impair or avoid rear end squat during maximum acceleration.
More recently, a type of drag racing traction bar has been provided which comprises a longitudinally disposed rigid beam secured to the axle housing with a forward portion of the beam clamped under the forward half of the vehicle leaf spring. This traction bar effectively transfers weight from the front end of the vehicle to the rear wheels as torque is applied while holding the chassis up and substantially eliminating axle wrap-up. However, the ride of the vehicle is substantially impaired by such a device due to the rigidifying of part of each leaf spring, and again, in the drag racing context, no compensation is provided for the torque reaction of the motor. Furthermore, clamping of the traction bar to the vehicle leaf spring causes stress concentrations in the spring that can lead to spring failure, particularly when the vehicle is put to relatively heavy use. It is also known to employ such a device with a single thrust surface associated with the forwardly extending end of the traction bar beam for contacting the bottom surface of the leaf spring during acceleration and preventing axle wrap-up as a result thereof. These devices allow the spring to deflect in the usual manner under normal load conditions to preserve the rideability of the car. However, these devices do not solve the axle wrap-up problem or wheel hop problem associated with rapid deceleration. Still others of these devices have been provided with pairs of thrust surfaces disposed at the forward end of the beam above and below the forward end of the vehicle leaf spring for allowing some longitudinal and vertical displacement of the leaf spring under normal road conditions to preserve the rideability of the vehicle. This helps prevent axle wrap-up during deceleration and the thrust surfaces may be adjustable to compensate for torque induced loading of the rear wheels during the type of acceleration encountered in drag racing. However, these drag racing type traction bars are unsuitable for use in conjunction with the spacing devices normally used in four-wheel drive vehicles for increasing the ground clearance and allowing the use of larger traction increasing tires. Furthermore, these devices do not increase the load carrying capacity of the vehicle leaf spring as is often necessary when a four-wheel drive vehicle is used for off road transportation or snow plowing.